Top-ranked Serena Williams avoided an early upset when she rallied from one set down to beat unheralded German Anna-Lena Friedsam 5-7, 6-3, 6-3 in the second round of the French Open on Thursday.

There was no such trouble for Rafael Nadal who eased into the third round of the men's draw with a 6-4, 6-3, 6-1 win against countryman Nicolas Almagro.

Seeking her 20th career Grand Slam title, and a third here at Roland Garros, Williams dropped her serve four times in her first ever match against Friedsam, ranked 105th.

Williams, the Australian Open champion, set up match point when she launched a huge forehand winner from the back of the court and followed that up with another big, cross-court forehand that flew out of the reach of Friedsam's outstretched racket.

Williams' relief was evident as she clenched her fist and let out a yell. She won here in 2013 and her other title was way back in 2002.

Although the sixth-seeded Nadal had to save a break point in his opening service game, and was not always at his fluent best with his shot-making, he stepped up a gear in a dominant third set to secure his 13th win in 14 matches against Almagro.

Almagro showed admirable defensive qualities, saving three set points in the opening set. Nadal clinched it on serve with a crisp forehand winner and then broke Almagro at the start of the second set.

After saving two break points in the ninth game, Nadal hit two clean aces to move 5-4 ahead.

Nadal, dressed head to toe in electric blue, stood out on center court in somewhat gloomy and overcast conditions. He sealed victory in 2 hours, 19 minutes when Almagro stretched to return a powerful forehand down the line and swiped the ball out of court.

Meanwhile, Francesca Schiavone of Italy again showed more endurance than 18th-seeded Svetlana Kuznetsova, beating her 6-7 (11), 7-5, 10-8 in a match lasting nearly four hours to reach the third round.

At the 2011 Australian Open, she beat the Russian player in the longest women's match, by time, in Grand Slam history — a 6-4, 1-6, 16-14 contest that lasted 4 hours, 44 minutes. Schiavone saved six match points in that match, then converted on her third match point.

It did not last quite so long this time — 3 hours, 50 minutes — but Schiavone, who is 34 years old and won the French Open in 2010, needed to save one match point at 6-5 in the third set with a brilliant backhand winner.

She sealed victory when Kuznetsova — a two-time Grand Slam champion who won here at Roland Garros in 2009 — attempted a forehand drop shot that sank into the net, bringing to an end a topsy-turvy match featuring brilliant winners but also some sloppy serving, with a total of 18 breaks of serve.

Schiavone tilted her head back in relief and then threw her arms up in the air in triumph after sealing victory.

Earlier, fifth-seeded Caroline Wozniacki of Denmark was knocked out after losing her second round match to Germany's Julia Goerges in straight sets.

Wozniacki, a former No. 1 and two-time finalist at the U.S. Open, has never advanced beyond the quarterfinals at the French and struggled throughout against the 72nd-ranked German.

Goerges advanced to the third round following a 6-4, 7-6 (4) win.

"I haven't beaten a top-10 player for a long time," Georges said. "I just told myself to be aggressive."

In the men's side of the draw, fifth-seeded Kei Nishikori of Japan became the first player to reach the second week of the tournament.

Nishikori was supposed to play Benjamin Becker in the third round on Friday, but Becker pulled out of the tournament Thursday because of a muscle tear in his right shoulder.

In other men's second-round play, U.S. Open champion Marin Cilic of Croatia, seeded ninth, had 10 aces as he advanced with a 7-6 (3), 6-1, 6-1 win against Italian qualifier Andrea Arnaboldi.

Leonardo Mayer of Argentina, seeded 23rd, won 6-4, 6-4, 6-7 (1), 6-1 against big-serving Jerzy Janowicz of Poland and Spaniard Pablo Andujar got the better of No. 22 Philipp Kohlschreiber of Germany 6-1, 7-6 (5), 3-6, 3-6, 6-4.

Top-ranked Novak Djokovic of Serbia was facing Luxembourg's Gilles Muller later Thursday and third-seeded Andy Murray was facing Portugal's Joao Sousa.

In other women's second-round play, two-time Wimbledon champion Petra Kvitova of the Czech Republic won 6-7 (4), 6-4, 6-2 against Silvia Soler-Espinosa of Spain, while No. 10 Andrea Petkovic of Germany — a semifinalist last year — also rallied to beat Spaniard Lourdes Dominguez Lino 4-6, 6-4, 6-4.